Re: [PATCH] ata: libata-scsi: set the field pointer when rejecting CDL

[Niklas Cassel <cassel@kernel.org>]

On Tue, Nov 03, 2026 at 10:04:18PM +0100, Niklas Cassel wrote:
> Hello Shao,
> 
> On Thu, Oct 29, 2026 at 07:03:14PM +0800, shao.mingyin@zte.com.cn wrote:
> > From: Shao Mingyin <shao.mingyin@zte.com.cn>
> > 
> > ata_mselect_control_ata_feature() rejects enabling CDL while NCQ
> > priority is enabled, but unlike its other error branches it returns
> > without setting *fp.
> > 
> > ata_scsi_mode_select_xlat() initializes fp to 0xffff and, when the
> > handler fails, adds the mode select header and block descriptor lengths
> > to it.  The resulting sense data then reports a field pointer far
> > outside of the submitted parameter list instead of the byte that has to
> > be changed.
> > 
> > Set *fp to the beginning of the mode page data, as the other branches of
> > this function do.
> > 
> > Fixes: df60f9c64576 ("scsi: ata: libata: Add ATA feature control sub-page translation")
> > Signed-off-by: Shao Mingyin <shao.mingyin@zte.com.cn>
> > ---
> > diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> > index 5cde90fe594e..c07c1ff09757 100644
> > --- a/drivers/ata/libata-scsi.c
> > +++ b/drivers/ata/libata-scsi.c
> > @@ -4494,6 +4494,7 @@ static int ata_mselect_control_ata_feature(struct ata_queued_cmd *qc,
> >  		if (dev->flags & ATA_DFLAG_NCQ_PRIO_ENABLED) {
> >  			ata_dev_err(dev,
> >  				"NCQ priority must be disabled to enable CDL\n");
> > +			*fp = 0;
> >  			return -EINVAL;
> >  		}
> >  		ata_dev_dbg(dev, "Enabling CDL\n");
> 
> 
> Setting fp to zero looks very wrong to me, even though with the current
> overly complicated code where buf and fp was using completely different
> offsets, it was actually correct.

Sorry, to clarify, 0 would have been wrong anyway, but because of existing
bugs in ata_scsi_mode_select_xlat() related to fp, not because your patch
was wrong:
https://lore.kernel.org/linux-ide/20261103205448.931471-10-cassel@kernel.org

  Parameter list                                     Before After Correct
  CDL enable while NCQ priority is enabled                7    12      12


Kind regards,
Niklas